1. Field of the Invention
This invention relates to the field of optoelectronics, which includes light emitting components, such as light emitting diodes (LED) and laser diodes, and which also includes light detecting components, such as photodiodes, phototransistors, photodarlingtons and photovoltaic cells. Optoelectronics also includes various devices which incorporate optoelectronic components, such as displays, photosensors, optocouplers, and fiberoptic transmitters and receivers. In particular, this invention relates to lenses to increase the efficiency of optoelectronic emitters and the sensitivity of optoelectronic detectors.
2. Description of the Related Art
A prior art LED 100 is shown in FIG. 1 and consists of a semiconductor diode element 110 electrically connected to a leadframe 120 and surrounded by an encapsulating material 130. The diode element 110 is typically mounted to one lead 122 of the leadframe 120 and connected to a second lead 124 of the leadframe 120 by a wire bond 140. These two leads provide an electrical connection between an external current source and the anode and cathode of the diode element 110. The external current source supplies power to the diode device 100 that is converted to emitted light by the photoelectric effect, which occurs at the semiconductor junction within the diode element 110.
Internal inefficiencies within a semiconductor diode result in very low net efficiencies, which is the ratio of emitted light power to input power. Internal inefficiencies arise from a low ratio of minority carriers injected into the diode semiconductor junction to photons generated at the junction; photon loss due to internal reflection at the semiconductor/encapsulant interface; and absorption of photons within the semiconductor material. Because of these low net efficiencies, many LED applications require high input current, resulting in heat dissipation and device degradation problems in order to obtain sufficient light.
As illustrated in FIG. 1, the encapsulant 130 forms a flat light-transmitting surface 150. A flat surface is convenient in many applications where the LED is mounted to another surface that is also generally flat or in applications that otherwise cannot accommodate a protruding surface. The inefficiencies described above, however, are compounded by the configuration of the LED encapsulant/air interface. An encapsulant having a flat surface, such as in FIG. 1, allows photons transmitted by the diode element 110 to have considerable dispersion. A flat encapsulant surface also results in internal reflection at the encapsulant/air interface, further reducing photon transmission and increasing photon absorption within the encapsulant material.
FIG. 2 illustrates a prior art LED 200 having an encapsulant 230 that forms a spherical surface 250. A spherical or other curved surface gives a larger angle of incidence for photons emitted from the semiconductor diode element 210, reducing losses due to internal reflection. Further, this surface 250 acts as a lens to reduce the dispersion of generated photons. Unfortunately, a protrusion, such as this curved surface, is difficult to accommodate in many applications.